Hi Robert, I've juried several shows and I can tell you that there's no by-the-numbers way to do it. (Actually there is, but the outcome usually is ridiculous when the results come from a checklist.) The best solution is to immerse yourself in visual art. Look at everything you can. Take the Great Courses (now too few) offerings in art. You judge a show pretty much the same way you frame and shoot a street shot. Your immediate impression is the most important thing; not whether or not the photographer applied the rule of thirds, etc. The problem you'll then run into is that some by-the-book guy will hassle you about, say, the crop, the sharpness, the colors, the composition, etc. (Same responses we run into on LuLa in User Critiques.) Bop the guy on the head if you can, or to avoid an invasion by the cops, simply ignore him.
Good luck. Judging art is not a hassle-free thing to do.